Mercury, 24-Hour Urine
Total mercury passed in urine over 24 hours, mostly from inorganic or elemental mercury such as vapor from spills, fillings or work exposure.
AI-verified against cited sources. Awaiting expert reviewAlso called U-Hg 24hLOINC 6693-6
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What it is
Mercury is a metal found in some industrial settings, older thermometers and gauges, dental amalgam fillings and certain products. In fish it takes a different form, called methylmercury. Your body clears inorganic and elemental mercury mostly through urine. For this test you collect all of your urine for one full day, and the lab measures the total amount of mercury in it.
Why it matters
Breathing mercury vapor or having ongoing contact with inorganic mercury can affect the nervous system and the kidneys. A 24-hour urine test is one way to look at that kind of exposure. It does not measure methylmercury from fish, which is better checked in blood.
If it’s high
A higher result means more mercury is leaving your body than is typical. That can be a sign of contact with inorganic or elemental mercury. A contaminated sample can also give an unexpected result, so a repeat test is sometimes reasonable. How a given level affects a person varies a lot.
Common causes
- A sample contaminated by skin, dust or a container that was not trace-element-free
- Dental amalgam (silver) fillings, which usually add only a small amount
- Work that involves mercury, such as dentistry, gold mining or some manufacturing
- Broken thermometers, gauges or other liquid mercury spills
- Some skin-lightening creams and traditional remedies that contain mercury
- A sample collected after a chelating medicine
What can help
- Ask your clinician whether the result fits your history, and whether to repeat it in a certified trace-element-free container
- If you work with mercury, ask about workplace exposure monitoring and protective equipment
- Follow local public-health guidance for cleaning up liquid mercury spills
- Check skin-lightening creams and traditional remedies for mercury on the label
- Ask whether a blood mercury test would add information, especially if you eat a lot of fish
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: up to 2 µg/24 h. Source: Mayo Clinic Laboratories (via the testcatalog.org mirror), ARUP Laboratories.
- 18+ (this one applies)up to 2 µg/24 h
Sources: Mayo Clinic Laboratories (via the testcatalog.org mirror), ARUP Laboratories
What can affect your result
- Collecting every void for the full 24 hours
- Seafood in the days before and during the collection
- Recent contrast dye (gadolinium or iodine)
- The number of dental amalgam fillings
- Work, hobby or home exposure to mercury
- The collection container and how the sample was kept
- Seafood in the 2 to 3 days before and during collection. Mayo asks you to avoid it for 48 hours, and ARUP for 48 to 72 hours.
- Gadolinium or iodine contrast dye can interfere with this kind of metal test. Mayo Clinic Laboratories asks for a 96-hour wait after contrast, and ARUP asks for at least 72 hours (14 days if kidney function is reduced).
- A sample contaminated by skin, dust or a container that is not certified trace-element-free can read falsely high. Labs may ask for a repeat in a certified container.
- Urine collected after a chelating (metal-binding) medicine, called a provoked or challenge test, has no valid reference range.
- An incomplete collection (a missed void) makes the 24-hour total too low.
- ARUP lists diet, supplements, vitamins and minerals as possible sources of interference. Ask your clinician before stopping anything.
Weeks to months. Inorganic mercury leaves the body slowly.
When to talk to a clinician
Talk with your clinician soon if your result is above your lab's range, especially if you work with mercury or have a tremor, unusual irritability, memory or sleep trouble, heavy drooling or gum problems. If you may have breathed vapor from a large mercury spill and feel unwell, seek urgent care. Mayo Clinic Laboratories notes that toxicity is usually apparent at about 50 µg per 24 hours or more, but the level at which symptoms start varies widely between people.
Questions you could ask
- Is a 24-hour urine, a spot urine or a blood test the best fit for my situation?
- Could my job, hobbies or home be a source of mercury?
- Should we repeat the test in a certified trace-element-free container?
- Would a blood mercury test add anything for me?
Questions people ask
Why do labs use such different limits for 24-hour urine mercury?
Mayo Clinic Laboratories uses less than 2 µg per 24 hours, while ARUP lists up to 20 µg per day. Labs choose their limits differently. Compare your result with the range printed on your own report, and ask your clinician how to read it.
Do I need to avoid fish before this test?
Labs usually ask you to avoid seafood before and during the collection. Mayo asks for 48 hours and ARUP for 48 to 72 hours. Follow the instructions from your lab.
What is a provoked urine mercury test?
It is a urine test collected after taking a chelating medicine. Normal ranges don't apply to those samples, and the American College of Medical Toxicology recommends against using them. Talk with your clinician if one was suggested to you.
Show the science and sources
Units
- 1 µg/24 h = 1 µg/24 h
- 1 µg/24 h = 4.985 nmol/24 h
Open the 24-h Urine Mercury unit converter
For clinicians and researchers
Measured by ICP-MS (triple-quadrupole at Mayo Clinic Laboratories HMU24, ICP-MS at ARUP). Urine mercury predominantly reflects elemental and inorganic mercury exposure, and ARUP recommends whole blood for acute exposure; methylmercury from fish is better assessed in blood. Labs differ about tenfold on the upper limit: Mayo below 2 µg/24 h in adults, ARUP up to 20.0 µg/day (and 5.0 µg/L, 20.0 µg/g creatinine). ARUP states that unexposed people typically have urine mercury below 10 µg/L, that 24-hour concentrations of 30 to 100 µg/L may be associated with subclinical neuropsychiatric symptoms and tremor, and that above 100 µg/L can accompany overt neuropsychiatric disturbance. Mayo gives about 50 µg/24 h as the lowest level at which toxicity is usually apparent, with wide variation between patients. Mayo asks that the 24-hour specimen be refrigerated within 4 hours of finishing, in a plastic container with no metal parts. Post-chelator challenge urine testing has no valid reference range, and the American College of Medical Toxicology recommends against it. The creatinine-corrected result (a separate marker) can help judge whether a collection was complete.
LOINC 6693-6 (primary), 25471-4. Specimen: urine-24h.
Sources
- Heavy Metals Screen, with Reflex, 24 Hour, Urine (test HMU24), Mayo Clinic Laboratories (via the testcatalog.org mirror)
- Mercury, Urine (test 0025050), ARUP Laboratories
- ACMT Recommends Against Use of Post-Chelator Challenge Urinary Metal Testing, American College of Medical Toxicology (Journal of Medical Toxicology) (2017)
- Mercury (compound summary), PubChem, National Library of Medicine
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.